It is well known to those skilled in the art that polyurethane foams can be prepared by reacting and foaming a mixture of ingredients, consisting in general of an organic polyisocyanate and an appropriate amount of polyol or mixture of polyols in the presence of a volatile liquid blowing agent, which is caused to vaporize by the heat liberated during the reaction of the polyisocyanate and polyol. It is also well known that this reaction and foaming process can be enhanced through use of amine and metal carboxylate catalysts as well as surfactants. The catalysts ensure adequate curing of the foam while the surfactants regulate and control cell size.
In the class of foams known as low density, rigid polyurethane foam, the blowing agents of choice early on had been trichlorofluoromethane and dichlorodifluoromethane, known in the art as CFC-11 and CFC-12, respectively.
Due to the concern over the depletion of the ozone layer by chlorine atoms introduced to the atmosphere from the release of fully halogenated chlorofluorocarbons (CFCs), alternative blowing agents have been sought. Hydrochlorofluorocarbons (HFCs) such as HCFC-141b have been allowed temporarily to displace the CFCs. The HCFCs will in turn be phased out in favor of more environmentally acceptable hydrofluorocarbons (HFCs).
However, organic substances which bear a hydrogen on one carbon and a fluorine on an adjacent carbon will undergo elimination reactions under the influence of acids or bases to produce fluoroalkenes and hydrogen fluoride or products from the combination of the hydrogen fluoride with the base, known as salts.
Therefore, in view of the fact that some of the major and many of the minor components, e.g. polyols and catalysts, are of known basic character, dehydrofluorination of the HFCs might occur. Many of these fluoroalkenes possess unknown properties and it is therefore desirable to hold their formation to a minimum as a precautionary measure.
U.S. Pat. No. 5,668,834 discloses catalysts which stabilize hydrohalocarbon blowing agents in polyurethane foam formulations.